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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

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21 g

oxygen still present are eliminated by passing the gas through a glass or
porcelain tube containing platinised asbestos heated to redness, the water
formed being absorbed by means of a U-tube charged with phosphoric
anhydride.

Prior to the determination, a blank test is made, the hydrogen being
passed through the glass or porcelain tube to be used in the determination
and arranged on a combustion furnace ; after about 10 minutes, a tared
phosphoric anhydride tube, full of hydrogen and connected with a calcium
chloride tube to keep atmospheric moisture away, is attached, the tube
being then heated to redness and the stream of hydrogen continued for
about an hour. At the end of thfs time the burners are extinguished and
the tube allowed to cool in the current of hydrogen ; the U-tube should
exhibit no appreciable increase in weight.

For the determination, 10 grams of the sample, freed from grease and
any traces of iron (see i) are weighed in a perfectly dry porcelain boat,
which is placed in the cold, dry combustion tube, the air being then expelled
by passing hydrogen for 10-15 minutes. The phosphoric anhydride tube
and its calcium chloride tube are then attached and the tube heated strongly
near the boat for 20-30 minutes.

When the reduction is complete, the tube is allowed to cool in the current
of hydrogen and the phosphoric anhydride tube weighed ; the increased
weight represents water, and this should correspond with the oxygen lost
from the metal in the boat.

The determination of oxygen in copper is a very delicate and perhaps not
quite exact operation. Metallographic examination gives information in this
respect.

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* *

Copper of good quality should be bright red and very ductile and malleable ;
its fracture should be finely granular, of uniform colour and free from spots ;
its specific gravity should lie between 8-65 and 8-93, and it should contain more
than 99-5% Cu (electrolytic copper may contain 99-8-99-9% or even more).
As the purity diminishes, the specific gravity, malleability and ductility
decrease.

Of the likely impurities, those of special influence on the mechanical pro-
perties are bismuth, lead, antimony, sulphur, arsenic, phosphorus, nickel, iron
and oxygen.

According to Hampe, the presence of 0-02% Bi is sufficient to render copper
brittle in the hot, while 0-05% makes it brittle also in the cold. Keller states
that copper containing a few thousandths of bismuth is unsuitable for electrical
conductors ; a similar effect is exerted by lead in the proportion of 0-3-0-4%.
Antimony was once regarded as highly injurious, but less than 0-5% appears
innocuous ; in whatever proportion, it lowers the electrical conductivity, and
copper containing antimony is unfit for making brass. Sulphur, which may be
present as cuprous sulphide, renders it cold short if present in greater quantity
than 0-5%. On the other hand, phosphorus and arsenic in small proportions
(not more than 0-5%) make it more tenacious and resistant, because they impede
the formation of cuprous oxide, 0-5% of which greatly diminishes the tenacity
and ductility (some types of copper may contain even more, electrolytic copper
according to Keller, as much as 0-6-0-8%). On this account, certain railway
companies use for their locomotive boilers copper containing not less than 0-2-
0-3% of arsenic. Small proportions of iron and nickel may often be found inso be added.o